Large balloons

Anderson’s 1957 Fort Churchill expedition As Kinsey Anderson was arriving in Iowa City in September 1955, our summer rockoon expedition was returning with new information about the auroral soft radiation. When Kinsey saw those results, he noted that the anomalous radiation was occasionally penetrating to altitudes lower than the rockets’ peak altitudes. In fact, the auroral soft radiation was sometimes seen at altitudes that might be reachable directly by Skyhook balloons. He believed that balloon flights, flown for extended periods of 10 to 30 hours at their peak altitudes, might be able to capture synoptic and time variation information on both the auroral soft radiation and low-energy cosmic rays that was not obtainable from the relatively short duration rockoon flights.

Kinsey had been impressed by a seminar at Minnesota in late 1954, in which Phyllis Freier described a potential IGY project for studying cosmic ray variations. She suggested that a series of balloon launches covering an extended period carry a standard set of cosmic ray particle detectors to study those variations.

CHAPTER 4 • THE IGY PROGRAM AT IOWA 97

Those two lines of thought converged, prompting Kinsey to submit a proposal to the U. S. National Committee for the IGY in November 1955. It called for a large number of high-altitude, long-duration balloon flights to be carried out during 1957 at Fort Churchill, Canada, a site well within the auroral oval.14

Kinsey immediately began designing an instrument to achieve that objective. It in­cluded three basic detectors: (1) a GM counter telescope, (2) a single GM counter, and (3) a scintillation detector using a thallium-activated sodium iodide crystal mounted on the front of a photomultiplier tube. The scintillation detector was configured to have high efficiency for X-ray radiation at energies above about 10 keV He expected the combination of instruments to reveal new information about the energy spectrum of the parent electrons that were responsible for the auroras.

However, Kinsey ran into serious problems in moving his project forward. To begin with, rules at the University of Iowa at that time did not permit junior researchers to submit proposals to outside agencies. Van Allen stepped in to sidestep that hurdle. The next step was to gain U. S. and IGY programmatic and financial support. In late 1955, Homer Newell’s Special Committee for the IGY (operating under the umbrella of the U. S. Upper Atmosphere Rocket Research Panel) reviewed his proposal and rejected it, apparently through some misunderstanding between Kinsey and the committee. Newell went so far as to declare that, beyond the funding issue, the U. S. military support group at Fort Churchill would not be permitted to support it.

Kinsey then attempted to obtain funding via the National Academy’s Technical Panel on Rocketry for the IGY. Scott E. Forbush, as its chairman, explained that nearly all of their funds for U. S. IGY cosmic ray research had already been committed. He asked if $15,000 would permit a useful program (compared with the $60,000 that Kinsey had requested). The panel also stated that, if approved, Kinsey would have to switch to a substantially different detector complement, to bring it more in line with programs at other locations that had already been approved. Specifically, it would have to include two instruments like those being used by the Minnesota group: a 10 inch diameter Neher-type integrating ionization chamber and their single GM counter design. Under those conditions, it would not be possible for Kinsey to in­clude the envisioned scintillation detector, and the nature of the project would be substantially different than originally envisioned.

Nevertheless, Kinsey quickly replied that he would be able to achieve meaningful results with that arrangement and submitted a revised proposal for the new instruments and a reduced number of flights. That resulted in approval for the modified program in April 1956.

Even then, the way was not clear. Newell had forbidden support by the U. S. military support at Fort Churchill, so other arrangements had to be made for launch­ing the balloons. Acting on Van Allen’s suggestion that he contact Donald C. Rose

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of the Canadian National Research Council, the problem was eventually resolved when Kinsey’s program was made part of the joint Canadian-U. S. IGY program, with Canada taking responsibility for the launches. Kinsey later reported that the arrangement with the Canadians turned out to be a very happy and productive one.

Developing the new instruments presented another major challenge to Kinsey, as he had no previous experience with ion chambers. With help from several students, and benefiting from the instrument shop’s much-earlier experience with Bob Ellis’ ion chambers (described in the first chapter), he prepared the instruments during 1956 and the first half of 1957. The spherical chambers had to be designed, manufac­tured, and assembled, and then they had to be baked out, evacuated, filled with argon gas, and calibrated (Figure 4.3). And the GM counters and various associated elec­tronics had to be designed and built. Completing the work was touch-and-go, and the last few ion chambers were completed only days before the first scheduled balloon launch.

With the various delays, final approval for the flights was not obtained until April 1957, only 10 weeks before the field operation was to begin. The schedule was met, however, and between 7 August and 7 September 1957, Kinsey, with help from three undergraduate students, directed the launch of 14 of his balloons from Fort Churchill. In total, they obtained about 175 hours of data from altitudes above 18 miles.

Kinsey related a fascinating tale about a highly improbable event that occurred during their field operation. In his words:

CHAPTER 4 • THE IGY PROGRAM AT IOWA

The program of IGY balloon launches in 1957 was punctuated by a remarkable coincidence in space, time, and people. After we had launched a balloon on 7 August, we hurriedly loaded the inflation gear into the panel truck and sped toward the main base and our telemetry station. The road closely paralleled the western shore of Hudson Bay. Glancing eastward over the Bay I saw a polyethylene research balloon coming out of a low-lying cloud layer. The balloon we had just launched had moved rapidly westward and away from Hudson Bay only a few minutes before. The intruder collapsed onto the rocky beach. We stopped the truck, started the Homelite generator, and snapped on our checkout telemetry receiver. We were indeed still receiving the VHF telemetry signal from our balloon off to the west. I then guessed that the interloper had to be a balloon used by the SUI group launching Rockoons in the Davis Strait half a continent away to the East. Running to the beach where the balloon lay partly in the water and partly on the beach, I chopped off the end portions with the hunting knife I carried (most persons engaged in launching large balloons carried such a knife believing it might save their life should they become fouled in a line as the balloon was released). When we returned to Iowa City, I showed the balloon ends to Laurence Cahill who verified they were from a balloon of the type used that summer for the Rockoon launches.15

Although most of Kinsey’s flights provided interesting and useful data, the one on 29 August 1957 was especially noteworthy. A Forbush decrease in cosmic ray intensity marking the beginning of a geomagnetic storm was detected by monitors at numerous ground locations while the balloon flight was in progress. The cosmic ray decrease at flight altitude was about twice as large as that observed on the ground. Although soft radiation (X-ray) was seen frequently throughout the flight, a strong burst of X-rays lasting about five minutes was seen in the balloon’s instrument at a time coinciding with the beginning of the storm. Ground observers reported that they had seen bright and active visible auroral during the period of observation. That was one of the earliest cases where the direct effect of energetic particles (electrons) was associated with such a geomagnetic phenomenon.

During flights on several other nights when quiet auroral arcs appeared in the sky, no similar X-rays were seen by the balloon instruments. This led to Kinsey’s inference that the quiet arc type of aurora did not involve electrons having energies high enough to produce X-rays that could penetrate that deeply into the atmosphere.16

Returning to Fort Churchill in 1958 Following up on his 1957 success, Kinsey proposed a series of balloon flights for August-September 1958 to further study the auroral zone radiation. Again, the balloons were to be launched from Fort Churchill. Approval was much more straightforward for that proposal—he submitted it to the U. S. National Committee for the IGY in October 1957, and it was approved relatively quickly.

Assisted by Donald Enemark, they made substantial improvements in the instru­ment design. They improved the low-temperature performance of transistor ampli­fying and scaling circuits, and the weight of the package was reduced by replacing the vacuum tube transmitter with one employing silicon transistors. In August, the

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two, joined by students Donald Stilwell and Louis Hinton, made their way to Fort Churchill with their instruments.

During the August-September 1958 period, they made 10 balloon flights, col­lecting 150 hours of high-altitude data. Kinsey’s account of the launch operations provides interesting reading.17 It tells of launches made during windy conditions from locations ranging from the leeward side of an aircraft hangar to the playground of the Fort Churchill elementary school, where many eager young faces watched from the windows. The flights produced varying results, with some indicating only quiet-time background cosmic radiation, while others showed moderate auroral X-ray activity.

The flight launched at about 8:30 local time the evening of 21 August was more exciting. By 10:30, the balloon had settled at its float altitude. Throughout the night, the counting rates were monotonously constant, revealing only the presence of the normal background cosmic rays. They were sufficiently uninteresting that Kinsey felt comfortable in catching a few hours’ sleep. After breakfast, he returned to the receiving station to find the situation unchanged. However, at about 9:45 on the morning of 22 August, things changed dramatically. The pen movements on the data recorder began to speed up—over several minutes, the rates climbed to previously unseen levels. All detectors were vigorously responding to some form of ionizing radiation. In Kinsey’s words:

I was especially struck by the rapid pulse rate of the usually sluggish ionization chamber.

Ionizing radiation was reaching the balloon at intensities far beyond anything that we had encountered on any previous flight. Recovering my composure, I began to think about what the detector responses were telling us. Careful study of the data received to that point convinced Donald Enemark and me that there were no instrument malfunctions. The ratio of the ion chamber to single counter response was much higher than could be produced by X-rays or gamma rays; therefore, the ionizing radiation could not be due to auroral associated X-rays.

The most powerful information for identifying the ionizing radiation came from the ion chamber-to-counter telescope ratio. That ratio told me the ionizing radiation could not be electrons, alpha particles, or heavier atomic nuclei. The measured ratio was just what I expected from fluxes of protons. After our return to Iowa City, I rechecked calibrations and made more detailed calculations and found the average energy of the protons arriving at our balloon over Fort Churchill, on 22 August 1958 to be 170 MeV.18

A highly varying pattern evolved over the next hours. The counting rates dropped and rose over a three hour period, and then the heavily ionizing radiation began a slow but steady decline. That continued throughout the rest of the morning and afternoon. Some protons were still present, however, when the transmission from the balloon ceased at about 5:00 in the afternoon of 22 August.

The team soon learned that an intense burst of radio noise was emitted from the Sun starting at about 8:15 AM, about 90 minutes before the protons were seen by the

CHAPTER 4 • THE IGY PROGRAM AT IOWA 101

balloon instruments. They also learned that a great solar flare had been observed to begin about 75 minutes before the proton arrival.

That event did not produce a measurable effect in ground neutron monitors, as did some other rather rare superflares, like the one that occurred on 23 February 1956. It was clear that the proton energies were too low for either the primary or the secondary particles to penetrate the atmosphere and reach the ground.

From his flights and the work of others, it soon became understood that the Sun produces, in addition to the huge flares previously seen, more frequent smaller flares that emit large fluxes of protons of much lower energies than those produced by the large ones. This new knowledge played an important role in the evolution of the thinking about solar processes and solar-terrestrial relationships.

McDonald to Missouri and Minnesota On 27 June 1958, with help from aide Louis Hinton, Frank McDonald flew a two million cubic foot Skyhook balloon from Moberly, Missouri, to study latitude variations of the cosmic ray heavy nuclei and their relation to the sunspot cycle. The instruments were recovered the next day, and Frank and Louis flew immediately to International Falls in northern Minnesota to fly them again there. Those observations further extended the latitude range of Frank and Bill Webber’s earlier heavy-nuclei observations.

And Anderson back to Canada Kinsey Anderson’s final Iowa balloon-launching expedition was to Resolute, on Resolute Bay, Cornwallis Island, Canada. He chose that location because of its nearness to the Earth’s north magnetic dip pole (the location of the north magnetic dip pole is considerably removed from both the north geomagnetic pole and the north geographic pole). On that expedition, in July 1959, Kinsey, Don Enemark, and Robert Lamb launched 10 balloons into very high intensities of particles produced by large solar flares.

Balloons as a continuing feature Balloon flights by the Iowa group continued throughout the rest of the decade, both with the huge Skyhook balloons and with much smaller ones.

Balloons are still in use today, primarily to achieve long flight durations at relatively low cost. Flight capabilities have grown dramatically since the 1950s. To illustrate, a new balloon flight duration and distance record was set in early 2005. It involved a flight of nearly 42 days, during which the balloon and its instruments traveled through three orbits around the South Pole. Launched from the National Science Founda­tion’s McMurdo Station in Antarctica on 16 December 2004, it landed on 27 January 2005 after traveling 27,410 miles. The enormous balloon, weighing 4055 pounds, ex­panded to a diameter of more than 450 feet at its ceiling height of 125,000 feet (about 24 miles). The balloon carried a Cosmic Ray Energetics and Mass experiment de­signed to explore the supernova acceleration limit of cosmic rays, the relativistic gas of protons, and electrons and heavy nuclei arriving at Earth from outside the solar

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system. That flight was an early demonstration of the developmental NASA Ultra­Long Duration Balloon, which is expected to extend flight times up to 100 days.19 Balloon sizes are now up to nearly 30 million cubic feet, capable of carrying payload weights exceeding 5000 pounds.20

Summarizing the Iowa experience with balloons during the decade of the 1950s, many Iowa physics students did at least part of their research with balloon-borne instruments. At first, very small, inexpensive latex balloons were used by graduate students Leslie Meredith, Robert A. Ellis Jr., Ernest C. Ray, Kenneth E. Buttrey, William R. Webber, and Raymond F. Missert. By the end of the decade, after the Skyhooks had entered the scene, many additional researchers had used balloons. They included (in addition to the work of McDonald, Kinsey Anderson, Cahill, and McIlwain described earlier) graduate students Hugh Anderson and Ralph Tuckfield. Many of those flights contributed significant new information about radiation in and above the Earth’s atmosphere.